This may reflect a higher salting out
effect of ammonium sulfate on papain owing to its higher surface
hydrophobicity as compared to the other proteases [18]. Consequently,
papain is preferentially partitioned to the top phase. This
is also in accordance with the relatively higher papain recovery
during ammonium sulfate precipitation reported in Table 1. As
seen in Table 2, increase in ammonium sulfate concentration
used to make the two-phase system increased only the recovery
of papain in the top phase but not that of total protease activity.
On the other hand, PEG concentration did not have any significant
effect on protease partitioning in general. Partitioning at
protein concentrations ranging between 10 and 40 mg protein/ml
in 12% PEG–15% (NH4)2SO4 revealed no notable variation in
protease partition to the top phase.